Evaporator with aerodynamic first dimples to suppress whistling noise

ABSTRACT

A heat exchanger assembly including a plurality of pairs of plates disposed in series for fluid flow from a pass through one pair of plates to a pass through the next pair of plates. Each pair of plates includes a central rib to define a U-shaped passage having a fluid entering leg and a fluid exiting leg interconnected by an open bottom interconnecting the legs below the lower end of the engaging ribs. A plurality of first dimples project into the passage to interact with fluid flow through the passage and each of the first dimples has an aerodynamic, e.g., tear-drop, shape to reduce whistling noise in the latter pairs of plates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat exchanger assembly, and more particularly, to an evaporator for a heating and/or air conditioning system (HVAC) for automotive vehicles.

2. Description of the Prior Art

An evaporator of the type to which the subject invention pertains exchanges heat between a cooling fluid and air. A stack of virtually identical plates are positioned symmetrically in pairs having mating edges and a concave region delimited by the edges to define a fluid passage. The plates have tubular projections defining an inlet for entering fluid to the passage and an outlet for exiting fluid from the passage to thereby establish a direction of fluid flow. Each inlet is connected to the outlet of the preceding pair of plates and each outlet is connected to the inlet of the next pair of plates. Actually, each pair of plates includes a central rib to define a U-shaped passage having a fluid entering leg and a fluid exiting leg interconnected by an open bottom. Examples of such heat exchangers are described in U.S. Pat. No. 5,111,878 to Kadle and U.S. Pat. No. 5,409,056 to Farry, Jr. et al.

Hot and humid air flows between the consecutive pairs of plates. The plates are usually stamped of thin gauge metal and a plurality of first dimples are stamped into the plates to project into the passage to interact with fluid flow through the passage. These first dimples can be identical in shape, position and orientation or they can be of various shapes as illustrated in U.S. Pat. No. 6,289,982 to Naji. They project into the interior of the passage formed by the pairs of plates and thus allow better heat exchange by agitating the cooling fluid flow, and especially by promoting its movement in a turbulent flow. These first dimples can be formed by an assembly method, particularly by brazing two bosses opposite each other. In this case, the plates forming a pair of plates are the same as one another, and each boss has an equivalent height of approximately one-half of the depth of the U-shaped passage, that is to say of the distance from the opposing plates.

Unfortunately the flow of cooling fluid in this type of evaporator can produce a noise, particularly a “whistling”, i.e., a tonal noise emanating from a plate-type evaporator used in certain automotive climate control systems under transient conditions. It is believed that this tonal noise occurs when gaseous refrigerant at sufficiently high velocities flows over the first dimples. It is further believed that the tonal noise is caused by periodic flow instability (manifested as vortices) in the wake of the first dimples. When the vortex shedding frequency is near the natural frequency of the gas column perpendicular to the direction of flow, a strong acoustic oscillation of the vapor column is excited, and it is this resonant oscillation that is believed to be the source of the tonal noise or whistle.

SUMMARY OF THE INVENTION AND ADVANTAGES

The invention resides in each of the first dimples having an aerodynamic shape including a large bulbous leading portion extending into a longer and tapering trailing portion with the leading portion being disposed into the fluid flow from the inlet to the outlet.

The aerodynamic first dimples of this invention will suppress or eliminate the instability that is produced in the dimple wake when gaseous refrigerant flows over the first dimples. An additional advantage of the aerodynamic first dimples of this invention is a reduction in refrigerant pressure drop. By providing the aerodynamic first dimples of the subject invention in combination with the regular dimples of other shapes, i.e., providing the aerodynamic first dimples in selected positions, flow-induced transient tonal noise, such as whistles, are suppressed without significantly sacrificing cooling capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a plurality of pairs of plates incorporating the subject invention in a heat exchanger assembly;

FIG. 2 is a cross sectional perspective view taken along line 2-2 of FIG. 1;

FIG. 3 is an exploded perspective view of two pairs of plates employed in the heat exchanger of FIGS. 1 and 2; and

FIG. 4 is an elevational view of one plate incorporating the subject invention and

FIG. 5 is an elevational view of one plate using known dimples for use in passes prior to the passes in which the subject invention is incorporated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A heat exchanger assembly is variously shown in the Figures and includes as a basic component at least one pair 20 of plates 22. The plates 22 can be identical and disposed in mirror relationship to one another. The plates 22 have mating edges 24 and a concave region delimited by the edges 24 to define a fluid passage 26. The assembly includes a plurality of pairs 20 of the plates 22 disposed in series for fluid flow from a pass through one pair 20 of plates 22 to a pass through the next pair 20 of plates 22, as illustrated by the arrows in FIG. 3. Each pair 20 of plates 22 includes a central rib 28 to define a U-shaped passage 26 having a fluid entering leg and a fluid exiting leg interconnected by an open bottom interconnecting the legs below the lower end of the engaging ribs 28. The plates 22 have tubular projections 30 defining an inlet for entering fluid to the passage 26 and an outlet for exiting fluid from the passage 26 to thereby establish a direction of fluid flow, as indicated by the arrows in FIGS. 1 and 4.

As is well known, the heat exchanger assembly normally includes air-fins 32 disposed between adjacent pairs 20 of plates 22 for enhancing heat exchange between air flowing (as shown by the air flow arrow in FIG. 1) through the air-fins 32 and fluid flow through the passage 26 defined by each pair 20 of plates 22. As shown in FIG. 2, additional fluid-fins 34 may be disposed in the fluid passages 26 although in the preferred embodiment such internal fins would not be included.

A plurality of first dimples 36 project into the passage 26 to interact with fluid flow through the passage 26 and each of the first dimples 36 has an aerodynamic shape including a large bulbous leading portion extending into a longer and tapering trailing portion with the leading portion being disposed into the fluid flow from the inlet to the outlet. The aerodynamic shape of each of the first dimples 36 is tear-drop shaped.

The first dimples 36 are combined in use with a plurality of second dimples 38 having different shapes. The second dimples 38 comprise known regular or bluff-body shapes to enhance the uniform distribution of liquid refrigerant over the plates 22 and, therefore, the heat transfer. The first dimples 36 are disposed in at least a selected section of the last pair 20 of plates 22 defining the last pass of fluid flow through the entire heat exchanger assembly. The first dimples 36 may also be disposed in at least the last two pairs 20 of plates 22 defining the last two passes. The first dimples 36 are combined with the second dimples 38 in the pair 20 of plates 22 defining the last pass. The use of aerodynamic dimples reduce heat transfer due to less intense turbulence, however, very desirable results are produced by using two kinds of dimples. The regular (or bluff-body) dimples in the earlier passes are designed to enhance the uniform distribution of liquid refrigerant over the tube plate and therefore the heat transfer. FIG. 5 shows the round dimples 38 combined with oval or oblong dimples in earlier passes. The aerodynamic dimples in the last pass or last two passes or in selected tubes thereof (which typically experience high vapor superheats and velocities), are intended to suppress acoustic resonance. More specifically, the first dimples 36 are disposed in the legs and not in the bottom of the U-shaped passage 26 while the second dimples 38 are disposed in the bottom of the U-shaped passage 26 below the bottom end of the mating ribs 28. Since the flow-induced instabilities are directly related to dimple geometry, this invention proposes “aerodynamic” or “tear-drop shaped” dimples in the last refrigerant pass (or last two passes) of the evaporator. In other words, this invention proposes the disposition of aerodynamic or tear-drop shaped first dimples 36 in the last refrigerant pass defined by the last pair 20 of plates 22, or in the last two pairs 20 of plates 22, or in selected sections (e.g., above the bottom-end of the mating ribs 28 of the last one or two passes as defined by the last two pairs 20 of plates 22, it being appreciated that the dimples 36 could be used in any number or combination of passes.) The aerodynamic first dimples 36 suppress acoustic resonance in the last pass or last two passes where high vapor superheats and high velocities typically occur to cause acoustic resonance. The combination of the aerodynamic first dimples 36 with the normal second dimples 38 provides a balance between heat transfer and noise reduction.

Each first dimple 36 has an axis A and extends equally on either side of and along the axis A. In addition, each axis A is disposed at an acute angle Φ from the direction of fluid flow. Furthermore, the first dimples 36 are disposed in overlapping relationship in the direction of fluid flow.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims. 

1. A heat exchanger assembly comprising; at least one pair of plates having mating edges and a concave region delimited by said edges to define a fluid passage, said plates having tubular projections defining an inlet for entering fluid to said passage and an outlet for exiting fluid from said passage to thereby establish a direction of fluid flow, a plurality of first dimples projecting into said passage to interact with fluid flow through said passage, and characterized by each of said first dimples having an aerodynamic shape including a large bulbous leading portion extending into a longer and tapering trailing portion with said leading portion being disposed into the fluid flow from said inlet to said outlet.
 2. An assembly as set forth in claim 1 wherein said aerodynamic shape of each of said first dimples is tear-drop shaped.
 3. An assembly as set forth in claim 1 including a plurality of pairs of said plates disposed in series for fluid flow from a pass through one pair of plates to a pass through the next pair of plates.
 4. An assembly as set forth in claim 3 wherein said first dimples are disposed in at least a selected section of said pair of plates defining the last pass.
 5. An assembly as set forth in claim 3 wherein said first dimples are disposed in at least the last two pair of plates defining the last two passes.
 6. An assembly as set forth in claim 3 wherein said first dimples are disposed in a first section and combined with a plurality of second dimples having different shapes in said pair of plates defining the last pass.
 7. An assembly as set forth in claim 3 wherein each first dimple has an axis A and extends equally on either side of and along said axis A, each axis A being disposed at an acute angle Φ from said direction of fluid flow.
 8. An assembly as set forth in claim 7 wherein said first dimples are disposed in overlapping relationship in said direction of fluid flow.
 9. An assembly as set forth in claim 3 wherein each of said pair of plates includes a central rib to define a U-shaped passage having a fluid entering leg and a fluid exiting leg interconnected by an open bottom.
 10. An assembly as set forth in claim 9 wherein said first dimples are disposed in said legs and not in said bottom of said U-shaped passage.
 11. An assembly as set forth in claim 9 wherein each first dimple has an axis A and extends equally on either side of and along said axis A, each axis A being disposed at an acute angle Φ from said direction of fluid flow.
 12. An assembly as set forth in claim 11 wherein said first dimples are disposed in overlapping relationship in said direction of fluid flow.
 13. An assembly as set forth in claim 3 wherein said first dimples are disposed in a first section and combined with a plurality of second dimples having different shapes in said pair of plates defining the last pass, and including air-fins disposed between adjacent pairs of plates for enhancing heat exchange between air flowing through said fins and fluid flow through said passage defined by each pair of plates. 